The 42-year-old actor pushed Gellar's face into a cake in a video Monday after the actress reached two million followers on Instagram.
Gellar posted a clip of herself holding an Instagram-themed cake reading "Thank you 2M." Prinze appeared from offscreen after Gellar announced her achievement.
"Thank you so much for helping me smash two million on Instagram!" Gellar told her followers.
"Did you say smash?" Prinze said before pushing the actress' face into the cake.
Prinze and Gellar met on the set of the 1997 movie I Know What You Did Last Summer, and married in September 2002. Prinze shared the secrets behind their lasting marriage ahead of their 15-year wedding anniversary last year.
"We treat each other with respect, we didn't just get married because we thought the other was young and hot. I think that sort of crushes relationships a lot," the actor said.
"Sacrifice is something that's required in a marriage. It's fun being single, right? You can be selfish. But marriages require a step back from that and a bit of sacrifice, and our sacrifice I think is maybe the biggest thing that's made our marriage work," he added.
Prinze and Gellar are parents to 8-year-old daughter Charlotte Grace and 5-year-old son Rocky James. In addition to I Know What You Did Last Summer, the couple have co-starred in Scooby-Doo and its sequel.